Coated web with water vapor barrier resistance



May 16, 1961 c. c. SHERMAN 2,934,585

COATED WEB WITH WATER VAPOR BARRIER RESISTANCE Filed July 5, 1957 United States Patent COATED WEB WITH WATER VAPOR BARRIER RESISTANCE Clayton Carr Sherman, Hinsdale, Ill., assignor to H. P. Smith Paper Co., Chicago, 111., a corporation of Illinois Filed July 5, 1957, Ser. No. 670,288

3 Claims. (Cl. 117-76) This invention relates to webs and the coating thereof. More particularly, this invention is concerned with novel coated webs in sheet and roll form in which the web may be paper, paper board, fabric or other web-like bases.

Webs such as paper are, of course, Widely used in packaging operations. Paper, however, has very poor resistance to penetration by water vapor. To improve the water vapor transmission resistance paper has been coated with a variety of substances. The most common paper coating is wax. Wax coated paper, however, while it has good water vapor barrier transmission resistance in a smooth or uncreased condition, has poor resistance after it is creased. Apparently the brittleness of the wax is so great that creasing causes it to fracture and break thereby providing many areas through which water vapor can pass with little if any resistance.

Paper has also been coated with thin films of normally solid polyethylene, as shown in British Patent No. 701,553. The resulting polyethylene coated paper was found to have less resistance to water vapor penetration than wax coated paper when each was tested in a flat or smooth uncreased condition. However, in the creased state the polyethylene coated paper was a better barrier than the wax coated paper. Nevertheless, the water vapor resistance for the polyethylene coated paper is approximately the same in the creased and uncreased states.

The coating of paper with wax containing a small amount of a flexible plastic, such as polyethylene, was also tried but the coated paper had poor vapor resistance after it was creased.

A mixture of polyethylene (60%) and wax (40%) was also tried as a coating. Paper to which a film of this composition was applied by extrusion was not as good when creased against water vapor permeability than a coating of polyethylene alone of the same weight.

When polyethylene is modified with a hot melt, such as wax, the water vapor transmission resistance of the coating after creasing is poorer than polyethylene alone. However, when a wax coating is modified by inclusion of polyethylene the water vapor resistance of paper coated with this material uncreased or flat is poorer than paper overcoated with wax alone in the uncreased state. The more a polyethylene coating is modified by the addition of wax, the poorer its water vapor transmission resistance becomes after creasing. The more a hot-melt overcoating, such as wax on paper, is modified by inclusion of polyethylene, the poorer its Water vapor transmission resistance becomes in the flat or uncreased condition.

I have now discovered, however, that when a web coated with a flexible polymeric coating of low water vapor transmission resistance, such as paper coated with polyethylene, is subsequently overcoated on the polymeric coating with a hot-melt coating substance of good vapor transmission resistance such as wax, the resulting coated web has excellent water vapor barrier properties. Furthermore, the water vapor transmission resistance of the ICC paper so coated is greater than the additive water vapor transmission resistances of each coating alone on paper. A synergistic effect is accordingly achieved.

As used herein the term hot-melt means material which forms a non-viscous melt upon heating which can be applied onto the surface of a polymeric substance, such as polyethylene, previously applied to a web such as paper without adverse eifect to the Web or polymeric substance. The term hot-melt further means those materials which when molten wet the surface of polyethylene and thereby form a molecularly adherent overcoating thereon.

The physical processes employed to coat the paper with polyethylene and to overcoat the polyethylene with wax are not the subject of this invention. Processes are now available and well known for accomplishing such results. The application of Wax to polyethylene coated sheets or finished objects such as cartons may be accomplished by known methods.

The application of a light overcoat of wax to a film of polyethylene on paper, or to a self-sustaining web of polyethylene, may be accomplished by many conventional means. When the thickness of wax is great it may be desirable to use a Mayer machine. The preferred lightweight coatings may be applied by running the polyethylene coated paper web or the free polyethylene film between two rolls one of which feeds the molten wax, or by dipping the polyethylene coated paper web or the free polyethylene film into molten wax followed by passage through a pair of squeeze rolls to limit the wax to the proper thickness, or by passing the polyethylene coated paper web through molten wax maintained between the nip of two squeeze rolls. Obviously, the passage of the coated paper or the film through a bath of wax, whether maintained independently or between the nip of two rolls, permits simultaneous coating of wax on both sides of the coated paper or the film and normally will not be used unless there is a polyethylene coating on both sides of a paper web or it is desired to coat both sides of the polyethylene film.

The invention is illustrated in the drawings in which Figure l is a diagrammatic sectional view of the polyethylene coated paper with a hot-melt i.e. wax, overcoat, the relative thicknesses being necessarily greatly exaggerated and Figure 2 is a similar view of free polyethylene film with a wax overcoat.

As shown in the drawings, 10 represents a paper backing which may be a continuous web or a sheet or a formed article; 11 represents a polyethylene coating thereon and 12 a molecularly adherent overcoat on the polyethylene.

As shown in Figure 2, the base 13 is a polyethylene film which may be in continuous form or in sheets and 14 is the molecularly adherent overcoat, preferably of parafiin wax.

By suitable arrangement of the coating equipment it is feasible to apply the polyethylene coat to a web such as paper and immediately thereafter apply the hot-melt coat to the polyethylene surface so that the web is coated in one continuous operation.

The polyethylene coated web such as paper which may be coated according to this invention to produce a product of enhanced vapor barrier characteristics may contain from about 0.5 to 87 pounds of polyethylene on one side per ream. (A ream is 3000 sq. ft. and equals 500 sheets, 24 inches by 36 inches.) Generally, however, about 1-10 pounds of polyethylene per ream is adequate while l-4 pounds is all that is needed for many uses.

The amount of hot-melt coat, such as waxes like paraffin and microwaxes, or a hydrogenated fat applied to the polymeric coat may be varied considerably. In

general, however, the economical useful range is about 0.1 to 15 pounds of a hot-melt such as wax per ream on 4 the combination of a polyethylene coat and a wax coat of only /3 the weight had excellent barrier properties.

Table 1 Water Vapor Transmission Rate (grams Composition of Material of water that pass 100 Coating oating Costs, sq. in. area in 24 hrs. Barrier Coating Description Weight, Dollars! at 100 F. and 90% to lbs/ream Thousand 95% relative humidity) stl uage Poly- W ee ethylene, Flat Greased Percent Percent Polyethyleneextrusion coated, Vs mil. 3 100 0.35 6. 75 7. 0803) (A) Polyethylene-extrusion coated, t In 7.2 100 0 0. 84 3.8 3.8 (A) Polyethylene-extrusion coated, 1 mil. 14. 4 100 0 1.68 1 1-1. 2 1. 1-1. 2 (A) Param.nMayer Machine Applied l2 0 100 0. 35 0 3-0. 7 20. 0-30.0 PolyethyleneParaffin Mixture, Mayer Mac plied 15 5 95 0. 49 0. 4-0. 6 8. 0-12. 0(B) (A) Polyethylene-Paratfin Mixture, Extrusion Ooated 15 60 40 1. 60 0.7-0.9 1. 0-1. 5 Polyethylene Coating (extrusion coated) plus Parafiin Coating (Squeeze roll applied) 3. 7 81 19 0. 37 0.38 0. 64(B) (A) Published data.

(B) APPARATUS 1- r s surface, Consisting f a flat rect l r pl te (cg, a piece of machined metal plate about 0.25 inch thick or a piece of plate glass) whose width shall be at least linch greater than the length of the specimens to be creased.

2. Creasing Platen, consisting of a suitably loaded, flat, square, metal or glass plate whose length is about 0.5 inch greater than that of the specimens to be creased. Its weight in kilograms shall equal the length in centimeters of the specimens to be creased (in pounds, approximately six times the length in inches). For convenience, a handle for carrying and raising the platen should be provided.

3. Flat Strip of Wood or Metal to give the specimen a preliminary light crease.

TEST SPECIMEN Test specimens, obtained according to TAPPI Standard T 400m, are cut into 6inch squares having edges parallel to the principal directions of the material and of suitable size for enabling a disk for the water vapor permeability test to be cut from each. The specimens are conditioned according to TAPPI Standard T 402m,-in a controlled atmosphere of 73 F. and 50% RH for at least 16 hours.

PROCEDURE The creases are made in an atmosphere conditioned according to TAPPI Standard T 402m. Two adjacent edges of the square specimen are marked ofi at uniform intervals approximately 2.0 inches apart, so that the two divisions along each edge are symmetrically spaced with the center of the specimen. The specimen is folded across at the first mark parallel to the adjacent edge and the fold lightly creased by presslng a flat strip of wood or metal upon it. The creasing platen is raised and the folded specimen slipped under it and parallel to its edge until the fold lies under the center of gravity of the platen. The platen is gently lowered to rest on the specimen, left for to seconds and then removed. The specimen is unfolded, then folded and a new crease made parallel to the first crease at the mark along the edge. 0n the opposite side of the sample the entire process is repeated along the adjacent edgeto produce a similar set of creases intersecting the first set at right angles.

Using a circular template or cutter, the specimen is trimmed into a circle of the desired size or the Water vapor permeability apparatus, the center of the circle so out being situated at the middle of the center square formed by the creases.

one side of a web such as paper. For most purposes about 0.5 to 2 pounds of hot-melt per ream is adequate. Waxes having melting points from about 110 F. to 250 F. may be used as the hot-melt although generally waxes melting at 120-175 F. are employed. Refined paraffin melting at about 135137 F. is particularly satisfactory.

The water vapor transmission rates of paper of essentially the same weight coated with (l) polyethylene of various weights applied by extrusion, (2) parafiin applied by Mayer machine, (3) a parafiin-polyethylene (95% to 5% mixture), applied by Mayer machine, (4) a 60% polyethylene-40% paraflin mixture applied by extrusion, (5) and a polyethylene coating (melt index 8.3; density at 23 C., 0.9235) applied by extrusion over which a paraffin wax coating (M.P. 135137 F.) was applied by a rubber squeeze roll, are set forth in Table I following. Some of this data is from published sources. All of the data was obtained, however, by the TAPPI Standard T-448rn Test except for certain of the data on creased samples for which a modified, more stringent preparation of samples was used as defined below. No data for uncoated paper is presented because it is such a poor water vapor barrier that it cannot be evaluated by the test procedures.

The test data of Table I shows the substantial superiority of paper coated with polyethylene over which wax is applied as a water vapor transmission barrier. These results indicate a synergistic effect since the water vapor transmission resistance of the polyethylene coated-wax coated paper is greater than that of the values for the individual coats applied alone on paper. Such a coat gives better performance than coats of polyethylene alone, or polyethylene mixed with wax, which are 4 times as heavy and significantly more expensive. The .paraffin coat alone is seen to be very poor in the crease test while While the invention has been described primarily in connection with paper as such, his not the intention to exclude from the invention the application of polyethylene with an adherent hot-melt overcoating such as wax to the heavier papers or paper boards. In cases where the paper itself is so thick as not to be readily creasable, it may be scored to provide creasability. Normally, however, the overcoating in such cases will be done after the polyethylene coated board or heavy paper has been die cut and scored for creasing.

Various changes and modifications of the invention can be made and, to the extent that such variations incorporate the spirit of this invention they are intended to be included within the scope of the appended claims.

What is claimed is:

1. A paper coated with about 0.5 to 87 pounds of polyethylene on one side, and 0.1 to 15 pounds of wax on the polyethylene coating, per each 3000 square feet of paper.

2. A paper coated with about 1 to 10 pounds of polyethylene on one side, and 0.1 to 15 pounds of wax on the polyethylene coating, per each 3000 square feet of paper.

3. A paper coated with about 1 to 4 pounds of polyethylene on one side, and 0.5 to 2 pounds of wax on the polyethylene coating, per each 3000 square feet of paper.

References Cited in the file of this patent UNITED STATES PATENTS 2,306,046 Duggan ct al. Dec. 22, 1942 2,642,366 Rumberger June 16, 1953 2,702,256 Trachet Feb. 15, 1955 2,714,571 Irion et al. Aug. 2, 1955 2,754,278 Wilson et al. July 10, 1956 2,758,100 Bailly et al. Aug. 7, 19 

1. A PAPER COATED WITH ABOUT 0.5 TO 87 POUNDS OF POLYETHYLENE ON ONE SIDE, AND 0.1 TO 15 POUNDS OF WAX ON THE POLYETHYLENE COATING, PER EACH 3000 SQUARE FEET OF PAPER. 